diff --git a/lib/cli/etcher.js b/lib/cli/etcher.js
index 77ffe11a..60fc5b11 100644
--- a/lib/cli/etcher.js
+++ b/lib/cli/etcher.js
@@ -74,8 +74,9 @@ permissions.isElevated().then((elevated) => {
   }
 
   const progressBars = new Map()
-  let lastStateType
+  let lastStateType = null
 
+  // eslint-disable-next-line require-jsdoc
   const onProgress = (state) => {
     state.message = state.active > 1
       ? `${bytes(state.totalSpeed)}/s total, ${bytes(state.speed)}/s x ${state.active}`
@@ -83,21 +84,25 @@ permissions.isElevated().then((elevated) => {
 
     state.message = `${state.type === 'flashing' ? 'Flashing' : 'Validating'}: ${state.message}`
 
+    // eslint-disable-next-line no-undefined
     if (state.percentage === undefined) {
       state.message += ` - ${bytes(state.bytes)} written`
     }
 
     // Update progress bar
     let progressBar = progressBars.get(state.type)
+    // eslint-disable-next-line no-undefined
     if (progressBar === undefined) {
       // Stop the spinner if there is one
-      if ((lastStateType !== undefined) && (lastStateType !== state.type)) {
+      if ((lastStateType !== null) && (lastStateType !== state.type)) {
         const spinner = progressBars.get(lastStateType)
+        // eslint-disable-next-line no-undefined
         if ((spinner !== undefined) && (spinner instanceof visuals.Spinner)) {
           console.log()
           spinner.stop()
         }
       }
+      // eslint-disable-next-line no-undefined
       if (state.percentage === undefined) {
         progressBar = new visuals.Spinner(state.message)
         progressBar.start()
@@ -106,12 +111,10 @@ permissions.isElevated().then((elevated) => {
         progressBar.update(state)
       }
       progressBars.set(state.type, progressBar)
+    } else if (progressBar instanceof visuals.Spinner) {
+      progressBar.spinner.setSpinnerTitle(state.message)
     } else {
-      if (progressBar instanceof visuals.Spinner) {
-        progressBar.spinner.setSpinnerTitle(state.message)
-      } else {
-        progressBar.update(state)
-      }
+      progressBar.update(state)
     }
     lastStateType = state.type
   }
@@ -125,28 +128,28 @@ permissions.isElevated().then((elevated) => {
     scanner.on('error', reject)
     scanner.start()
   })
-  .then(() => {
-    return (new sdk.sourceDestination.File(imagePath, sdk.sourceDestination.File.OpenFlags.Read)).getInnerSource()
-  })
-  .then((innerSource) => {
-    // NOTE: Drive can be (String|Array)
-    const destinations = [].concat(answers.drive).map((device) => {
-      const drive = scanner.getBy('device', device)
-      if (drive === undefined) {
-        throw new Error(`No such drive ${device}`)
-      }
-      return drive
+    .then(() => {
+      return (new sdk.sourceDestination.File(imagePath, sdk.sourceDestination.File.OpenFlags.Read)).getInnerSource()
+    })
+    .then((innerSource) => {
+      // NOTE: Drive can be (String|Array)
+      const destinations = _.map([].concat(answers.drive), (device) => {
+        const drive = scanner.getBy('device', device)
+        if (!drive) {
+          throw new Error(`No such drive ${device}`)
+        }
+        return drive
+      })
+      return sdk.multiWrite.pipeSourceToDestinations(
+        innerSource,
+        destinations,
+        (destination, error) => {
+          console.log(`Error "${error}" on ${destination.drive}`)
+        },
+        onProgress,
+        options.check
+      )
     })
-    return sdk.multiWrite.pipeSourceToDestinations(
-      innerSource,
-      destinations,
-      (destination, error) => {
-        console.log(`Error "${error}" on ${destination.drive}`)
-      },
-      onProgress,
-      options.check
-    )
-  })
 }).then(({ failures, bytesWritten }) => {
   let exitCode = EXIT_CODES.SUCCESS
 
diff --git a/lib/gui/app/app.js b/lib/gui/app/app.js
index 48dc93f7..0912227a 100644
--- a/lib/gui/app/app.js
+++ b/lib/gui/app/app.js
@@ -232,13 +232,13 @@ app.run(() => {
   })
 })
 
-
 app.run(($timeout) => {
   const BLACKLISTED_DRIVES = settings.has('driveBlacklist')
     ? settings.get('driveBlacklist').split(',')
     : []
 
-  function driveIsAllowed(drive) {
+  // eslint-disable-next-line require-jsdoc
+  const driveIsAllowed = (drive) => {
     return !(
       BLACKLISTED_DRIVES.includes(drive.devicePath) ||
       BLACKLISTED_DRIVES.includes(drive.device) ||
@@ -246,7 +246,8 @@ app.run(($timeout) => {
     )
   }
 
-  function prepareDrive(drive) {
+  // eslint-disable-next-line require-jsdoc,consistent-return
+  const prepareDrive = (drive) => {
     if (drive instanceof sdk.sourceDestination.BlockDevice) {
       return drive.drive
     } else if (drive instanceof sdk.sourceDestination.UsbbootDrive) {
@@ -261,9 +262,10 @@ app.run(($timeout) => {
     }
   }
 
-  function setDrives(drives) {
-    drives = _.values(drives)
-    availableDrives.setDrives(drives)
+  // eslint-disable-next-line require-jsdoc
+  const setDrives = (drives) => {
+    availableDrives.setDrives(_.values(drives))
+
     // Safely trigger a digest cycle.
     // In some cases, AngularJS doesn't acknowledge that the
     // available drives list has changed, and incorrectly
@@ -271,32 +273,37 @@ app.run(($timeout) => {
     $timeout()
   }
 
-  function getDrives() {
+  // eslint-disable-next-line require-jsdoc
+  const getDrives = () => {
     return _.keyBy(availableDrives.getDrives() || [], 'device')
   }
 
-  function addDrive(drive) {
-    drive = prepareDrive(drive)
-    if (!driveIsAllowed(drive)) {
+  // eslint-disable-next-line require-jsdoc
+  const addDrive = (drive) => {
+    const preparedDrive = prepareDrive(drive)
+    if (!driveIsAllowed(preparedDrive)) {
       return
     }
     const drives = getDrives()
-    drives[drive.device] = drive
+    drives[preparedDrive.device] = preparedDrive
     setDrives(drives)
   }
 
-  function removeDrive(drive) {
-    drive = prepareDrive(drive)
+  // eslint-disable-next-line require-jsdoc
+  const removeDrive = (drive) => {
+    const preparedDrive = prepareDrive(drive)
     const drives = getDrives()
-    delete drives[drive.device]
+    // eslint-disable-next-line prefer-reflect
+    delete drives[preparedDrive.device]
     setDrives(drives)
   }
 
-  function updateDriveProgress(drive, progress) {
+  // eslint-disable-next-line require-jsdoc
+  const updateDriveProgress = (drive, progress) => {
     const drives = getDrives()
-    const drive_ = drives[drive.device]
-    if (drive !== undefined) {
-      drive.progress = progress
+    const driveInMap = drives[drive.device]
+    if (driveInMap) {
+      driveInMap.progress = progress
       setDrives(drives)
     }
   }
diff --git a/lib/gui/app/models/store.js b/lib/gui/app/models/store.js
index 13c336bd..19756d37 100644
--- a/lib/gui/app/models/store.js
+++ b/lib/gui/app/models/store.js
@@ -24,7 +24,6 @@ const constraints = require('../../../shared/drive-constraints')
 const supportedFormats = require('../../../shared/supported-formats')
 const errors = require('../../../shared/errors')
 const fileExtensions = require('../../../shared/file-extensions')
-const utils = require('../../../shared/utils')
 const settings = require('./settings')
 
 /**
@@ -46,7 +45,7 @@ const verifyNoNilFields = (object, fields, name) => {
     return _.isNil(_.get(object, field))
   })
   if (nilFields.length) {
-    throw new Error(`Missing ${name} fields: ${nilFields.join(', ')} ${JSON.stringify(object, null, 4)}`)
+    throw new Error(`Missing ${name} fields: ${nilFields.join(', ')}`)
   }
 }
 
@@ -162,7 +161,7 @@ const storeReducer = (state = DEFAULT_STATE, action) => {
 
       const drives = action.data
 
-      //if (!_.isArray(drives) || !_.every(drives, _.isPlainObject)) {
+      // If (!_.isArray(drives) || !_.every(drives, _.isPlainObject)) {
       if (!_.isArray(drives)) {
         throw errors.createError({
           title: `Invalid drives: ${drives}`
@@ -407,6 +406,7 @@ const storeReducer = (state = DEFAULT_STATE, action) => {
 
       const MINIMUM_IMAGE_SIZE = 0
 
+      // eslint-disable-next-line no-undefined
       if ((action.data.size !== undefined) && (action.data.size < MINIMUM_IMAGE_SIZE)) {
         throw errors.createError({
           title: `Invalid image size: ${action.data.size}`
diff --git a/lib/gui/app/modules/drive-scanner.js b/lib/gui/app/modules/drive-scanner.js
index 3de66c2c..7a624411 100644
--- a/lib/gui/app/modules/drive-scanner.js
+++ b/lib/gui/app/modules/drive-scanner.js
@@ -21,7 +21,16 @@ const process = require('process')
 
 const settings = require('../models/settings')
 
-function includeSystemDrives() {
+/**
+ * @summary returns true if system drives should be shown
+ * @function
+ *
+ * @returns {Boolean}
+ *
+ * @example
+ * const shouldInclude = includeSystemDrives()
+ */
+const includeSystemDrives = () => {
   return settings.get('unsafeMode') && !settings.get('disableUnsafeMode')
 }
 
@@ -31,6 +40,7 @@ const adapters = [
 
 // Can't use permissions.isElevated() here as it returns a promise and we need to set
 // module.exports = scanner right now.
+// eslint-disable-next-line no-magic-numbers
 if ((process.platform !== 'linux') || (process.geteuid() === 0)) {
   adapters.push(new sdk.scanner.adapters.UsbbootDeviceAdapter())
 }
diff --git a/lib/gui/app/modules/progress-status.js b/lib/gui/app/modules/progress-status.js
index 6e2dae99..de0875fa 100644
--- a/lib/gui/app/modules/progress-status.js
+++ b/lib/gui/app/modules/progress-status.js
@@ -59,11 +59,11 @@ exports.fromFlashState = (state) => {
 
     return 'Finishing...'
   } else if (isFlashing) {
+    // eslint-disable-next-line no-eq-null
     if (state.percentage != null) {
       return `${state.percentage}% Flashing`
-    } else {
-      return `${units.bytesToClosestUnit(state.position)} flashed`
     }
+    return `${units.bytesToClosestUnit(state.position)} flashed`
   } else if (isValidating) {
     return `${state.percentage}% Validating`
   } else if (!isFlashing && !isValidating) {
diff --git a/lib/gui/app/os/window-progress.js b/lib/gui/app/os/window-progress.js
index 0053cc69..2efb4c1e 100644
--- a/lib/gui/app/os/window-progress.js
+++ b/lib/gui/app/os/window-progress.js
@@ -90,7 +90,8 @@ exports.currentWindow = electron.remote.getCurrentWindow()
  * })
  */
 exports.set = (state) => {
-  if (state.percentage != null) {
+  // eslint-disable-next-line no-eq-null
+  if (state.percentage !== null) {
     exports.currentWindow.setProgressBar(utils.percentageToFloat(state.percentage))
   }
   exports.currentWindow.setTitle(getWindowTitle(state))
diff --git a/lib/gui/app/pages/main/controllers/image-selection.js b/lib/gui/app/pages/main/controllers/image-selection.js
index 1a73b98e..5962a209 100644
--- a/lib/gui/app/pages/main/controllers/image-selection.js
+++ b/lib/gui/app/pages/main/controllers/image-selection.js
@@ -159,35 +159,36 @@ module.exports = function (
 
     const source = new sdk.sourceDestination.File(imagePath, sdk.sourceDestination.File.OpenFlags.Read)
     source.getInnerSource()
-    .then((innerSource) => {
-      return innerSource.getMetadata()
-      .then((metadata) => {
-        return innerSource.getPartitionTable()
-        .then((partitionTable) => {
-          if (partitionTable !== undefined) {
-            metadata.hasMBR = true
-            metadata.partitions = partitionTable.partitions
-          }
-          $timeout(() => {
-            metadata.path = imagePath
-            metadata.extension = path.extname(imagePath).slice(1)
-            this.selectImage(metadata)
+      .then((innerSource) => {
+        return innerSource.getMetadata()
+          .then((metadata) => {
+            return innerSource.getPartitionTable()
+              .then((partitionTable) => {
+                if (partitionTable) {
+                  metadata.hasMBR = true
+                  metadata.partitions = partitionTable.partitions
+                }
+                $timeout(() => {
+                  metadata.path = imagePath
+                  // eslint-disable-next-line no-magic-numbers
+                  metadata.extension = path.extname(imagePath).slice(1)
+                  this.selectImage(metadata)
+                })
+              })
+          })
+          .catch((error) => {
+            const imageError = errors.createUserError({
+              title: 'Error opening image',
+              description: messages.error.openImage(path.basename(imagePath), error.message)
+            })
+            osDialog.showError(imageError)
+            analytics.logException(error)
+          })
+          .then(() => {
+            return innerSource.close()
+              .catch(_.noop)
           })
-        })
       })
-      .catch((error) => {
-        const imageError = errors.createUserError({
-          title: 'Error opening image',
-          description: messages.error.openImage(path.basename(imagePath), error.message)
-        })
-        osDialog.showError(imageError)
-        analytics.logException(error)
-      })
-      .then(() => {
-        return innerSource.close()
-        .catch(() => {})
-      })
-    })
   }
 
   /**
diff --git a/lib/gui/modules/child-writer.js b/lib/gui/modules/child-writer.js
index d76f76bd..eba81709 100644
--- a/lib/gui/modules/child-writer.js
+++ b/lib/gui/modules/child-writer.js
@@ -16,7 +16,6 @@
 
 'use strict'
 
-const Bluebird = require('bluebird')
 const _ = require('lodash')
 const ipc = require('node-ipc')
 const sdk = require('etcher-sdk')
@@ -86,44 +85,67 @@ const handleError = (error) => {
   terminate(EXIT_CODES.GENERAL_ERROR)
 }
 
-function lastMapValue(map) {
-  let value
-  for (value of map.values()){
+/**
+ * @summary returns the last value in a Map
+ * @param {Map} map - map
+ * @returns {Any} the last value of the map (in insertion order)
+ *
+ * @example
+ * const last = lastMapValue(map)
+ */
+const lastMapValue = (map) => {
+  let value = null
+  for (value of map.values()) {
+    // eslint-disable-next-line no-empty
   }
   return value
 }
 
-function writeAndValidate(source, destinations, verify, onProgress, onFail, onFinish, onError) {
+/**
+ * @summary writes the source to the destinations and valiates the writes
+ * @param {SourceDestination} source - source
+ * @param {SourceDestination[]} destinations - destinations
+ * @param {Boolean} verify - whether to validate the writes or not
+ * @param {Function} onProgress - function to call on progress
+ * @param {Function} onFail - function to call on fail
+ * @param {Function} onFinish - function to call on finish
+ * @param {Function} onError - function to call on error
+ * @returns {Promise<void>}
+ *
+ * @example
+ * writeAndValidate(source, destinations, verify, onProgress, onFail, onFinish, onError)
+ */
+const writeAndValidate = (source, destinations, verify, onProgress, onFail, onFinish, onError) => {
   return source.getInnerSource()
-  .then((innerSource) => {
-    return sdk.multiWrite.pipeSourceToDestinations(
-      innerSource,
-      destinations,
-      onFail,
-      onProgress,
-      verify,
-    )
-  })
-  .then(({ failures, bytesWritten }) => {
+    .then((innerSource) => {
+      return sdk.multiWrite.pipeSourceToDestinations(
+        innerSource,
+        destinations,
+        onFail,
+        onProgress,
+        verify
+      )
+    })
+    .then(({ failures, bytesWritten }) => {
     // If all destinations errored, treat the last fail as an error
-    if (failures.size === destinations.length) {
-      throw lastMapValue(failures)
-    }
-    const result = {
-      bytesWritten,
-      devices: {
-        failed: failures.size,
-        successful: destinations.length - failures.size,
-      },
-      errors: []
-    }
-    for (const [ destination, error ] of failures) {
-      error.device = destination.drive.device
-      result.errors.push(error)
-    }
-    onFinish(result)
-  })
-  .catch(onError)
+      if (failures.size === destinations.length) {
+        throw lastMapValue(failures)
+      }
+      const result = {
+        bytesWritten,
+        devices: {
+          failed: failures.size,
+          successful: destinations.length - failures.size
+        },
+        errors: []
+      }
+      for (const [ destination, error ] of failures) {
+        error.device = destination.drive.device
+        result.errors.push(error)
+      }
+      onFinish(result)
+    })
+    .catch(onError)
 }
 
 ipc.connectTo(IPC_SERVER_ID, () => {
@@ -152,8 +174,6 @@ ipc.connectTo(IPC_SERVER_ID, () => {
     terminate(EXIT_CODES.SUCCESS)
   })
 
-  let writer = null
-
   ipc.of[IPC_SERVER_ID].on('write', (options) => {
     /**
      * @summary Progress handler
@@ -209,19 +229,21 @@ ipc.connectTo(IPC_SERVER_ID, () => {
 
     /**
      * @summary Failure handler (non-fatal errors)
-     * @param {Object} error - MultiDestinationError
+     * @param {SourceDestination} destination - destination
+     * @param {Error} error - error
      * @example
      * writer.on('fail', onFail)
      */
     const onFail = (destination, error) => {
       ipc.of[IPC_SERVER_ID].emit('fail', {
-        device: destination.drive,  // TODO: device should be destination
+        // TODO: device should be destination
+        device: destination.drive,
         error: errors.toJSON(error)
       })
     }
 
     const destinations = _.map(options.destinations, 'device')
-    const dests = options.destinations.map((destination) => {
+    const dests = _.map(options.destinations, (destination) => {
       return new sdk.sourceDestination.BlockDevice(destination, options.unmountOnSuccess)
     })
     const source = new sdk.sourceDestination.File(options.imagePath, sdk.sourceDestination.File.OpenFlags.Read)
diff --git a/lib/shared/supported-formats.js b/lib/shared/supported-formats.js
index d526643a..280b0b3b 100644
--- a/lib/shared/supported-formats.js
+++ b/lib/shared/supported-formats.js
@@ -18,6 +18,7 @@
 
 const sdk = require('etcher-sdk')
 const _ = require('lodash')
+// eslint-disable-next-line node/no-extraneous-require
 const mime = require('mime')
 const path = require('path')
 
@@ -40,7 +41,7 @@ exports.getCompressedExtensions = () => {
   for (const [ mimetype, cls ] of sdk.sourceDestination.SourceDestination.mimetypes.entries()) {
     if (cls.prototype instanceof sdk.sourceDestination.CompressedSource) {
       const mtype = mime.getExtension(mimetype)
-      if (mtype != null) {
+      if (mtype !== null) {
         result.push(mtype)
       }
     }